This invention relates to a topsheet for a body fluids absorbent article such as a sanitary napkin or a disposable diaper and also to a method of making this topsheet.
It is well known to make a nonwoven fabric by subjecting a web of thermoplastic synthetic resin staple fibers each having a length of 20xcx9c70 mm to water jet streams of high pressure so that the fibers may be mechanically entangled and simultaneously liquid-permeable openings may be formed. The nonwoven fabric obtained in this manner can be used as the liquid-permeable topsheet of a sanitary napkin, a disposable diaper or the like. By such a method, the staple fibers tend to extend in parallel one to another along the direction in which the web travels. Consequently, the staple fibers extend closely in parallel one to another particularly along peripheral edges of the respective openings. These staple fibers thereby define correspondingly clear contours of the respective openings so far as these openings are oval openings each having a major axis extending along the direction in which the web travels and a minor axis extending orthogonally to the direction.
FIG. 8 shows an example of the porous nonwoven fabric 101 obtained by the above-mentioned method. As shown, the nonwoven fabric is formed with a plurality of oval openings 102 each having a major axis Axe2x80x94A extending in one direction and a minor axis Bxe2x80x94B extending in the direction orthogonal to the major axis Axe2x80x94A. It is now assumed that the nonwoven fabric 101 is pulled, for example, in the proximity of one (102a) of the openings 102 in the direction of the major axis Axe2x80x94A. A dimension of this opening 102a as measured in the direction of its major axis Axe2x80x94A is enlarged while a dimension thereof in the direction of its minor axis Bxe2x80x94B is reduced, with a result that this opening 102a may be deformed narrower as indicated by imaginary lines. If many of the openings 102 are deformed narrower like the opening 102a with their dimensions in the direction of their minor axes Bxe2x80x94B extremely reduced, the nonwoven fabric 101 can not satisfy its desired function. This is for the reason that the openings 102 can no more smoothly guide body fluids and a time during which the body fluids stay on the topsheet, creating a discomfortable feeling of wetness against a wearer of the article.
In view of the above problem, it is a object of the invention to provide a topsheet used in body fluids absorbent article so improved that a body fluid permeability is never affected even if the topsheet is pulled in either direction thereof.
The object set forth above is achieved, according to one aspect of the invention, by a liquid-permeable topsheet forming at least a part of body fluids absorbent article, the topsheet comprising: the topsheet having skin-contacting side and skin-noncontactable side intended to and not to come in contact with the skin of a wearer of the article, respectively, the topsheet being formed by a nonwoven fabric made of thermoplastic synthetic fibers each having a fineness of 0.1xcx9c10 deniers and a length of 20xcx9c70 mm and mechanically entangled so as to extend in parallel one to another substantially in one direction and to leave a plurality of liquid-permeable openings providing a total area larger than a total area provided by interstices of the entangled fibers; and the openings including a first group of openings each having a substantially oval shape defined by a major axis thereof extending substantially in parallel to the one direction and a minor axis thereof extending orthogonally to the one direction and a second group of openings each having a substantially oval shape defined by a minor axis thereof extending substantially in parallel to the one direction and a major axis thereof extending orthogonally to the one direction.
Preferably, the topsheet is formed with a plurality of ridges obliquely extending so as to intersect the one direction and protruding from the skin-noncontactable side toward the skin-contactable side.
Alternatively, the plurality of ridges may comprise a first group of ridges and a second group of ridges intersecting the first group of ridges.
According to still another embodiment, the first and second groups of openings comprise those formed in the first and second groups of ridges, respectively, and those formed in regions each defined by a pair of adjacent ridges belonging to the first group and a pair of adjacent ridges belonging to the second group.
The object set forth above is achieved, according to the second aspect of the invention, by a method for making a liquid-permeable topsheet defining at least a part of body fluids absorbent article, the method at least comprising the steps of:
a. continuously feeding a web of thermoplastic synthetic fibers each having a length of 20xcx9c70 mm and conveying the web in one direction;
b. directing a high pressure water jet streams onto the web being conveyed so as to entangle the fibers and simultaneously to form first group of liquid-permeable openings each having a major axis thereof extending substantially in parallel to the one direction and a minor axis thereof extending orthogonally to the one direction; and
c. subjecting the web formed with the first group of openings to a mechanical treatment so as to form a second group of openings each having a substantially oval shape defined by a minor axis thereof extending substantially in parallel to the one direction and a major axis thereof extending orthogonally to the one direction.
An alternative embodiment of the method may further comprises the step of forming, simultaneously with or after the treatment to form the openings, a plurality of ridges obliquely extending in parallel one to another so as to intersect the one direction in which the web is conveyed and to protrude from one side of the web.
According to still another embodiment of the method, the ridges obliquely extending so as to intersect the direction in which the web is conveyed comprise a first group of ridges extending in parallel one to another and a second group of ridges extending in parallel one to another so as to intersect the first group of ridges.
According to further another embodiment of the method, the mechanical treatment to form said openings may be any one of a embossing treatment and a debossing treatment of said web.